LONDON (AP) — Barclays, Britain’s second-biggest bank, vowed to fight almost half-billion dollars in fines for manipulating electricity prices in California and other western states, setting the stage for a courtroom battle with U.S. regulators.

The Federal Energy Regulatory Commission on Tuesday ordered the U.K.-based bank and four of its former traders to pay $453 million in civil penalties for fixing power prices between November 2006 and December 2008.

The U.S. energy watchdog also ordered Barclays to pay $34.9 million, plus interest, for what it described as “unjust profits” made on energy assistance programs for low-income families in Arizona, California, Oregon and Washington.

“We believe that our trading was legitimate and in compliance with applicable law,” the bank said in a statement, adding it had cooperated with the investigation.

“We intend to vigorously defend this matter,” Barclays said.

FERC has given Barclays 30 days to pay the penalties. If it does not, regulators can go to a federal district court to affirm the penalty amount assessed in the order.

The allegations will mark a fresh blow to the scandal-shaken bank. The bank’s new chief executive, Antony Jenkins, has made a point of saying that ethics matter as much to Barclays as the bottom line. The lender has faced a string of scandals costing it billions of pounds (dollars), and was fined by regulators in the U.S. and Britain for manipulating the London interbank offered rate, or LIBOR, the benchmark for trillions of dollars in loans — including some home mortgages.

The statement by U.S. regulators said that Barclays and the four traders — Daniel Brin, Scott Connelly, Karen Levine and Ryan Smith — took part in an “affirmative, coordinated and intentional effort to carry out a manipulative scheme.”

Connelly was ordered to pay $15 million; and Brin, Levine and Smith to pay $1 million each. The traders have since left Barclays.

The traders bought and sold electricity contracts to manipulate energy indexes and help Barclays profit from investments tied to those benchmarks, FERC said in the statement.

The U.S. regulators said that Barclays “traded fixed-price products not in an attempt to profit from the relationship between the market fundamentals of supply and demand, but instead for the fraudulent purpose of moving the Index price.”

The fines are the largest penalty imposed by the Commission since Congress gave it broader anti-manipulation authority in the Energy Policy Act of 2005.

Barclays contests what it described as a one-sided statement, arguing that it strongly disagreed with a FERC assessment “that does not reflect a balanced and full description of the facts or the applicable legal standard.”

Investors did not seem worried, however, with Barclays’ share price trading up 0.49 percent at 310 pence on Wednesday.